The wind has historically been one of the most widely used natural resources to provide the energy necessary to power our needs. Windmills are still used to harness the wind's energy to grind grains into flour. Sailboats and windsurfs use sails to capture the power of the wind to travel across water. Recent increases in the demand for energy, combined with the dwindling supplies of fossil fuels, have caused electrical utility companies to take a renewed look at alternative methods for producing electrical power.
One alternative method of producing electrical power involves the harnessing of wind energy by a wind turbine to drive an electromagnetic generator. Wind turbines typically use a series of blades fixed to the top of a tower to rotate a shaft about a horizontal axis. The blades have an aerodynamic shape, such that when wind blows across the surface of the blades a lift force is generated causing the blades to rotate the shaft about its axis. The shaft is connected, typically via a gearbox, to an electromagnetic generator located in a structure called a nacelle which is positioned behind the blades. The gearbox converts the rotation speed of the blades into a rotation speed usable by the generator to produce electricity at a frequency that is proper for the electrical grid it is providing power to. The nacelle houses a number of components which are needed in modern high capacity wind turbines. In addition to the aforementioned gearbox and electromagnetic generator, other components may include a yaw drive which rotates the wind turbine, various controllers such as load balancing systems, and a brake that may be used to slow the generator down.
Electromagnetic generators are well known in the prior art. Broadly, electromagnetic generators generate electricity by varying a magnetic field, which induces electrical current in an adjacent coil. The magnetic field source has traditionally been a permanent magnet, but electromagnets have also been recently used.
Prior art devices typically use a magnetic field source, which is disposed adjacent to a coil, such that a small air gap separates the two. Several such pairs of magnetic field sources and coils may be used in a single device to increase efficiency. Most prior art devices operate by either moving the magnetic field source relative to the coil, or by moving the coil relative to the magnetic field source, to generate magnetic field fluctuations (also referred to as “magnetic flux” or “flux”), and thereby induce electrical current into the coils. To that end, most prior art devices use a stator and a rotor, the stator housing the stationary component, and the rotor moving the other component relative to the stationary one.
Additionally, there are several prior art devices that utilize a magnetic field blocking device to generate a magnetic flux within coils or windings to induce electrical current therein. The magnetic field blocking device is typically a magnetic field impermeable disk which has magnetic field permeable portions cut out in tooth-like or window-like configurations. The disk is disposed in the air gap between the magnetic field source and the coil. The flux-blocking disk is rotated in such a way as to alternatively allow axial flux to pass through from the magnetic field source to the coil, or to redirect the axial flux away from the coil. Alternatively, the flux-blocking disk is held stationary, and one of the coils or magnetic field source are rotated. For examples of such prior art devices see U.S. Pat. Nos. 3,431,444, 3,983,430, 4,639,626, and 6,140,730.
A major disadvantage of such prior art devices is the axial orientation of the flux relative to the disk, which poses three main problems. First, the surface area across which axial flux is generated is limited by the radius of the disk. Second, the frequency of the induced electrical current varies across the length of the radius of the disk, due to the varying angular velocity of various points along the radius. Third, the impermeable portions of the disk are pulled by the magnetic field source, and the permeable portions are not pulled by the magnetic field source as they cross the air gap between the magnetic field source and the coil. This alternating pull causes the disk to resonate laterally away from its axis of rotation, which resonating motion will hereinafter be referred to as “wobble.” The wobble is proportionally related to the radius of the disc, the strength of the magnetic field, and the rotations-per-minute (rpm or rpms) at which the disc rotates, and is inversely related to the thickness of the disk. In order to minimize the wobble, efficiency is sacrificed by lowering rpm, increasing the air gap between the magnetic field source and the coils to accommodate a thicker disc, and/or reducing the radius of the disc and thereby the surface area across which flux is generated.
Accordingly, there exists a need for a more efficient electromagnetic generator capable of operating at relatively low rpm and producing electrical current with minimal efficiency loss due to disk wobble, small surface area across which flux is generated, and/or air gap size. The inventive concepts disclosed herein are directed to such an electromagnetic generator and to method of using thereof.